The present invention relates to orthopedic implants and to methods of making the same. More particularly, the present invention is directed to apparatus and methods of forming such implants from polymers and other resorbable materials during spinal or general orthopedic surgery.
Well known to those skilled in the art is the use of orthopedic implants to repair and treat bone defects, such as cracked and broken bones, as well as disorders of the skeletal system. Many of the orthopedic implants are formed primarily of metallic materials. Metallic implants have several disadvantages. First, a surgeon may not have at his disposal in the operating room an implant of the desired size and/or shape to fit the unique geometry of a patient""s body. Additionally, metallic implants exhibit a significant compressive modulus over cortical bone and stress-shield new bone growth to induce osteoporosis and/or osteopenia, thereby resulting in cortical bone that is prone to refracture. Moreover, after repair of the bone defect, the implant is no longer needed; thus, removal of the implant necessitates a second surgery.
More recently, new treatment methods and improved materials, including nonmetallic implants, have been used to treat bone defects. Non-metallic implants can remain in the body, or alternatively, implants can be made of selected materials that biodegrade or are resorbable over a period of time ranging from a few days to several years. The absorption of bioresorbable medical implants into the body over a period of time allows bone growth in and around the space once occupied by the implant, thereby enabling repair of the bone at the defect site.
Known synthetic biodegradable polymers include homopolymers of lactic acid (PLA) and glycolic acid (PGA) and copolymers d, l, d/l lactic acid (PLDLA) and poly(lactide-co-glycolide) (PLA/PGA). A variety of these polymers are commercially available and can be synthesized to have a glass transition temperature between about 35xc2x0 C. and about 65xc2x0 C. These polymers become pliable when heated above their glass transition temperature and can be molded into a desired size and/or shape. Below the glass transition temperatures, they exhibit suitable compressive modulus to be used as orthopedic implants. Further, the compressive modulus and the rate of degradation can be tailored for specific medical applications by varying the ratio to d to l optical isomers of lactic acid in PLA and the ratio of lactic acid to glycolic acid in poly(lactide-co-glycolide).
In light of the above-described state of the art, the need exists for methods by which a surgeon, after assessing the particular geometry into which the implant must fit, can form the desired implant from a polymer or other resorbable material during the orthopedic surgery. The present invention satisfies this need in a novel and non-obvious way.
One aspect of the invention described herein is the ability of the surgeon to form a sheet of polymer or resorbable material in the shape of a spinal or general orthopedic implant in the operating room at the time of surgery.
One form of the present invention contemplates creating an orthopedic support from a sheet of moldable material such as a polymer or other resorbable material, including but not limited to PLA, PLDLA, PGA, and PGA/PLA. The surgeon assesses the geometry of the patient""s body to determine the desired size and shape of the implant. The implant material is heated until it is above its glass transition temperature. The surgeon then forms it into the desired shape using an appropriate instrument and cools the material below its glass transition temperature. The material retains the desired shape.
Another form of the present invention contemplates a surgeon forming a moldable material into an orthopedic implant of a desired shape during surgery and positioning the implant in a patient to provide orthopedic support.
In another form, this invention provides apparatus for forming orthopedic implants from moldable material. Such apparatus enable the surgeon or operator to fashion implants specifically tailored to a patient""s unique skeletal geometry. Implants fashioned according to such apparatus include shapes having, for example, circular, rounded-rectangular, kidney-shaped, semi-rectangular, crimped-rectangular, and B-shaped cross-sections.
One object of the present invention is to provide a unique method of forming, in the operating room and at the time of surgery, orthopedic implants from moldable material.
Further objects, features, and advantages of the present invention will be apparent from the description and drawings contained herein.